Connecticut-based Northern Tier's website says its St. Paul Park refinery has a daily capacity of 92,500 barrels. The company lists 163 SuperAmerica convenience stores and 74 franchised stores, primarily in Minnesota and Wisconsin.

Almost 200 Northern Tier workers are covered by a collective bargaining agreement that expires at the end of the month. Their union said management has proposed eliminating jobs and cutting wages by up to 40 percent among other changes that would drive experienced workers away.

"We simply won't allow this company to put profits before the safety of our people. … If there is a strike, SuperAmerica customers will need to go elsewhere for fuel this winter," Local 120 Business Agent Chris Riley said in a news release.

Woodbury-based SuperAmerica, Northern Tier and Western Refining could not be reached for comment.